As described in Third Generation Partnership Project (3GPP) Fifth Generation (5G) Technical Specification (TS) 38.214 V15.1.0, for 3GPP New Radio (NR), the Physical Uplink Shared Channel (PUSCH) time-domain resource allocation is indicated in the scheduling Downlink Control Information (DCI). Four (4) bits in the DCI select one time-domain resource allocation entry out of sixteen (16) configured time-domain resource allocation configurations. These sixteen (16) time-domain resource allocation configurations are included in a configured table, which is referred to in 3GPP TS 38.214 V15.1.0 as table pusch-symbol Allocation and more generally referred to herein as a PUSCH table. Each configuration provides a slot offset value (K2) that indicates, relative to the slot in which the DCI is received, the slot or start slot for slot aggregation for which the time-domain resource allocation is valid. In addition, the PUSCH table also provides symbol allocation within the slot and Demodulation Reference Signal (DM-RS) mapping type, where the DM-RS mapping type can either be Type A or Type B. There exists a default PUSCH table that can be overwritten by System Information Block 1 (SIB1). Once a User Equipment (UE) has a dedicated configuration, the UE can receive yet another PUSCH table with dedicated Radio Resource Control (RRC) signaling.
In NR, uplink transmissions are timing advanced. Partly during random access and partly during the time alignment procedure, a UE receives a Timing Advance (TA) value by which the UE should advance its uplink transmission. The TA value received during initial access is relative to the downlink timing, whereas TA values received as part of time alignment procedure are relative to the last uplink transmission. The total TA value applied by the UE is the accumulative sum of all received TA values. TA is needed in an Orthogonal Frequency Division Multiple Access (OFDMA) system to ensure that uplink transmissions from served UEs are time-aligned upon arrival at the base station to maintain orthogonality among UEs.
In NR, the time-domain resource allocation specified in an uplink grant for a PUSCH transmission is specified at the base station (i.e., NR base station (gNB)) timing, i.e. without timing advance. The time-domain resource allocation included in the uplink grant (i.e., slot offset K2 plus start symbol within the slot) specifies the PUSCH start relative to the downlink slot in which the uplink grant is transmitted.
The time at the UE between start of the downlink slot when the uplink grant is received and the time when the uplink transmission starts is given by the indicated time minus the TA value. The UE needs a minimum processing time to decode the uplink grant and prepare the uplink transmission. This time is given in the NR specification and is based on the values in Table 1 below. The parameter μ in the tables below indicates the numerology (μ=1: 15 kilohertz (kHz), μ=2: 30 kHz, μ=3: 60 kHz, μ=4: 120 kHz), which is also referred to as the subcarrier spacing. If uplink and downlink have different numerologies (i.e., different μ values which means different subcarrier spacing), the smaller μ value is used. Based on the PUSCH preparation time (N2) value from the table, the minimum processing time is determined as follows:Tproc,2=(N2+d2,1+d2,2)·(2048+144)·κ·2−μUL·Tcwhere:                N2: PUSCH preparation time from Table 1        d2,1: If the first symbol of the PUSCH allocation consists of DM-RS only, then d2,1=0, otherwise d2,1=1.        d2,2: Accounts for a time difference between component carriers if different component carriers are configured and can have a time difference larger than zero. Otherwise zero.        κ=64        Tc=1/(4096·480e3)It is up to the base station (i.e., the gNB) to make sure the signaled time-domain resource allocation allows sufficient processing time at the UE after the UE applies the TA value.        
TABLE 1PUSCH preparation time for PUSCH timing capability 1.Capability 1 refers to the basic processing capability.μPUSCH preparation time N2 [symbols]010112223336
For the first time-aligned PUSCH transmission during the random access procedure, which is referred to as Msg3, the uplink grant is not provided in a DCI (i.e., not provided in a Physical Downlink Control Channel (PDCCH)). Rather, the uplink grant for Msg3 is provided in Msg2 (i.e., the Random Access Response (RAR) message) signaled in a Physical Downlink Shared Channel (PDSCH). It is more complicated to decode PDSCH than PDCCH.
PDSCH timing is based on the values in Table 2 below and determined according to the formula below:Tproc,1=(N1+d1,1+d1,2+d1,3)·(2048+144)·κ·2−μDL·Tcwhere:                N1: PDSCH processing time from Table 2        d1,1: If Acknowledgement/Negative Acknowledgement (ACK/NACK) is transmitted on PUCCH, d1,1=0. If ACK/NACK is transmitted on PUSCH, d1,1=1.        d1,2: Accounts for a time difference between component carriers if different component carriers are configured and can have a time difference larger than zero. Otherwise zero.        d1,3: For PDSCH Type A only and ending in the i-th symbol with i<7: d1,3=7−i, otherwise d1,3=0. This accounts for the fact that a short PDSCH requires a bit more time after it has been finished to finalize decoding than a longer PDSCH.        κ=64        Tc=1/(4096·480e3)        
TABLE 2PDSCH processing time for PDSCH processing capability 1.Capability 1 refers to the basic processing capability. It is unclearif NR Rel-15 will also define a more advanced (faster)processing capability.PDSCH decoding time N1 [symbols]No additional PDSCH DM-RSAdditional PDSCH DM-RSμconfiguredconfigured0813110132172032024
The minimum processing time for Msg3 PUSCH is therefore larger than for a regular PUSCH since the additional processing for PDSCH decoding in Medium Access Control (MAC) and layer 1 needs to be considered. The minimum processing time for Msg3 PUSCH is therefore given by:Tproc,Msg3=(N2+N1+d2,1+d2,2)·(2048+144)·κ·2−μUL·Tc+0.5 msThe value N1 is from Table 2 with additional DM-RS configured. The 0.5 millisecond (ms) is added to account for layer 2 processing.
Thus, there is a need for signaling a time-domain resource allocation for a Msg3 transmission on PUSCH that accounts for the larger processing time needed for decoding of the uplink grant for the Msg3 transmission received on PDSCH.